The present invention relates to a device for processing digital data, and more specifically, to a device for processing digital data that is to be employed in an arithmetic operation device for executing an arithmetic operation, such as an exposure control for a camera, based upon input data, such as film sensitivity, shutter speed, and the like.
Conventionally, an arithmetic operation device has employed a device for processing digital data in which the number of bits (or digits) representing an original data is reduced by deleting a predetermined part of the digital data when the digital data is inputted in order to reduce a load imposed on a CPU by simplifying input data, and to reduce manufacturing cost by simplifying an input means itself.
Nevertheless, conventional converting device produce an increased error to an intended control, and thus, are not suitable, because it executes an arithmetic operation in coarse steps by ignoring deleted parts of the digital data or continues the arithmetic operation by assuming that the deleted bit is set to a predetermined value.
As an example, an automatic setting of a film sensitivity executed based on a conventional DX input will be described.
FIG. 4 shows a film patrone on which a DX code is printed to indicate the film sensitivity. The DX code is separated into electric conductive portions and insulated portions within a range from R1 to R12. The electric conductive portions are composed of an exposed metal and the insulated portions are coated. Portions R1 and R7 are used as a ground, and the film sensitivity is represented by a combination of the range from R2 to R6.
When a full range film sensitivity is obtained from a camera, six signal pins (one of which is ground) corresponding to respective ISO ranges are used, and the camera reads ISO 25-5000 in 1/3 Ev steps as shown in Table 1. It should be noted that an APEX system (additive system of photographic exposure) is generally employed for calculating an exposure time. In this system, the exposure value Ev is described as follows. EQU Av+Tv=Bv+Sv=Ev
wherein Av is an aperture value, Tv is a time value (representing a shutter speed), Bv is a brightness value, Sv is a speed value (representing a film sensitivity), and Ev is an exposure value.
In the case of a low price camera, the number of signal pins are typically reduced to 4, so as to reduce manufacturing costs. Thus, a reading step is in 1 Ev increments, as shown in Table 2. In this case, a single Sv represents three different values of ISO, which is so coarse that a problem arises in accuracy, when it is applied to the exposure control of a single lens reflex camera.
If 5 pins are employed, as shown in Table 3, it is not possible to discriminate 1/3 Ev from 2/3 Ev. If they are indiscriminately rounded to any one side, a value which is actually 1+1/3 Ev is input as 1+2/3 Ev, for example, causing a maximum exposure error of 1/3 Ev.
Further, when a direction in which rounding is carried out is fixed to any one of 1/3 Ev or 2/3 Ev, a setting may be made to accept a less frequently used film sensitivity when the less frequently used film sensitivity and a more frequently used film sensitivity
TABLE 1 ______________________________________ DX PIN ISO 6 5 4 3 2 Sv ______________________________________ 25 1 0 1 1 1 3 32 0 1 1 1 1 3 1/3 40 0 0 1 1 1 3 2/3 50 1 0 1 1 0 4 64 0 1 1 1 0 4 1/3 80 0 0 1 1 0 4 2/3 100 1 0 1 0 1 5 125 0 1 1 0 1 5 1/3 160 0 0 1 0 1 5 2/3 200 1 0 1 0 0 6 250 0 1 1 0 0 6 1/3 320 0 0 1 0 0 6 2/3 400 1 0 0 1 1 7 500 0 1 0 1 1 7 1/3 640 0 0 0 1 1 7 2/3 800 1 0 0 1 0 8 1000 0 1 0 1 0 8 1/3 1250 0 0 0 1 0 8 2/3 1600 1 0 0 0 1 9 2000 0 1 0 0 1 9 1/3 2500 0 0 0 0 1 92/3 3200 1 0 0 0 0 10 4000 0 1 0 0 0 10 1/3 5000 0 0 0 0 0 10 2/3 ______________________________________
are to be selected. If a less frequently used film sensitivity is set for representing both the less frequently used film and the frequently used film, the possibility of causing an exposure error is increased.
TABLE 2 ______________________________________ PIN ISO 4 3 2 Sv ______________________________________ 25 1 1 1 3 32 1 1 1 3 40 1 1 1 3 50 1 1 0 4 64 1 1 0 4 80 1 1 0 4 100 1 0 1 5 125 1 0 1 5 160 1 0 1 5 200 1 0 0 6 250 1 0 0 6 320 1 0 0 6 400 0 1 1 7 500 0 1 1 7 640 0 1 1 7 800 0 1 0 8 1000 0 1 0 8 1250 0 1 0 8 1600 0 0 1 9 2000 0 0 1 9 2500 0 0 1 9 3200 0 0 0 10 4000 0 0 0 10 5000 0 0 0 10 ______________________________________
TABLE 3 ______________________________________ PIN ISO 6 4 3 2 Sv ______________________________________ 25 1 1 1 1 3 32 0 1 1 1 3 ? 40 0 1 1 1 3 ? 50 1 1 1 0 4 64 0 1 1 0 4 ? 80 0 1 1 0 4 ? 100 1 1 0 1 5 125 0 1 0 1 5 ? 160 0 1 0 1 5 ? 200 1 1 0 0 6 250 0 1 0 0 6 ? 320 0 1 0 0 6 ? 400 1 0 1 1 7 500 0 0 1 1 7 ? 640 0 0 1 1 7 ? 800 1 0 1 0 8 1000 0 0 1 0 8 ? 1250 0 0 1 0 8 ? 1600 1 0 0 1 9 2000 0 0 0 1 9 ? 2500 0 0 0 1 9 ? 3200 1 0 0 0 10 4000 0 0 0 0 10 ? 5000 0 0 0 0 10 ? ______________________________________